Our conceptual frameworks of the processes that control carbon (C) stabilization in soil organic matter (SOM) are currently undergoing a major revision. Older theoretical models hold that SOM is comprised of recalcitrant plant-derived compounds, which are stabilized due to their inherent chemical complexity. In contrast to these long-held paradigms, new analytical techniques are revealing that most “old” soil C is comprised of simple, microbially-derived organic molecules which are stabilized on mineral surfaces. Despite this exciting new evidence, the mineralogical and microbial processes that govern the transformation of plant C inputs into stable SOM are still poorly understood. In this session, we will discuss new evidence for interacting microbial and mineralogical controls over SOM formation. Speakers will explore the relationships among microbial physiology, soil mineralogy, and SOM with multiple complimentary techniques, including infrared spectroscopy, in-situ isotope labeling experiments, soil metagenomics, and simulation models. The session will synthesize both empirical and theoretical advances, taking a multi-scale approach that integrates processes occurring within individual soil pores with ecosystem-scale and global C fluxes.